The present invention relates to a blind person guide device, and more particularly to a guide device having an infrared range finder or sonar for giving distance information to a blind person to help the blind person in walking safely.
Blind persons use walking sticks as an aid for walking safely. The walking stick gives the blind person direct information on dangerous objects existing in a range that can be reached by the walking stick. The walking stick also gives indirect information about the position of a nearby obstacle based on the echo of a click generated when it hits a hard ground, the echo being reflected from a relatively large object such as a wall positioned in a short distance from the blind person. An experiment indicates that a blind person with a walking stick can recognize a screen in a long hallway at a distance of 2 m from the screen. The principle is the same as ultrasonic echo sounding utilized by bats and dolphins. The source of sound for blind persons can be a footstep or a rustling sound of the clothes in addition to the walking stick.
However, if an object is small or positioned at a distance, then it is difficult to get correct information of the object with such an echo sounding principle. Desired distance information cannot be gained unless some aids such as a sonar or a range finder is used. Various means for measuring the distance to an object have been known. Some rely on electromagnetic or ultrasonic radiation to measure a distance based on a time required for the wave to reach an object, a wave interference, or triangulation. The known ranging devices are large in size and expensive, and need a highly accurate mechanism. The ultrasonic range finder is particularly disadvantageous in that since ultrasonic radiation spreads in a wide angle, information on a bearing is difficult to obtain and the distance up to a small object cannot be measured.
There is known as a walking aid for blind persons a device for enabling the blind person to recognize an object as a sound image. More specifically, the device operates by applying a signal from a range finder to a voltage-controlled oscillator and a voltage-controlled amplifier which produces a sound dependent on the distance to an object through an earphone. The person using this device can find a distance by recognizing an intensity of the sound, or a pitch of the sound, or both.
Blind persons have a very sharp sense of hearing. Therefore, wearing an earphone even on one ear would interfere with the normal activity to listen to ambient direct sounds. There has also been proposed to incorporate a sonar and a loudspeaker in a walking stick so that a sonar sound will be generated by the loudspeaker. While sounds from the loudspeaker can easily be heard in a room, they cannot clearly be heard unless they are louder in an open space. The sound from the loudspeaker in the walking stick has the advantages of attracting the attention of other people, but some blind persons do not want to attract too much attention. The blind also have a sharp sense of touch as indicated by the fact that they can read braille points by their fingertip.
Ultrasonic ranging devices include a device for varying the sound frequency dependent on the distance to an obstacle or a device having a plurality of ultrasonic transducers for producing a sound image indicative of the distance and bearing of an obstacle based on the localization of a sound source as perceived by the sense of hearing. With these ultrasonic devices, information is transmitted aurally to blind persons, and ambient sounds are masked so that the amount of information carried by the ambient sounds is reduced. Therefore, the total amount of information perceived by a blind person is not increased. The ultrasonic ranging devices also have the problem of consuming a large current. For the reasons described above, the ultrasonic ranging devices are not suitable as walking aids. Furthermore, when blind people free themselves from the ultrasonic ranging devices, they tend to forget to turn off the power supply switch and it is not easy for them to confirm whether the power supply switch is turned off or not.